kernel: move source and build output to work-shared

commit 3b3f7e785e279 [kernel: Rearrange for 1.8] began the process of
moving the kernel source and build artefacts out of sstate control and
into a shared location.

This changed triggered some workflow issues, as well as bugs related
to the kernel source containing build output, and hence being dirty and
breaking kernel rebuilds.

To solve these issues, and to make it clear that the kernel is not under
sstate control, we move the source and build outputs to:

  work-shared/MACHINE/kernel-source
  work-shared/MACHINE/kernel-build-artifacts

Where kernel-build-artifacts is the kernel build output and
kernel-source is kept "pristine". The build-artifacts contain everything
that is required to build external modules against the kernel source,
and includes the defconfig, the kernel-abiversion, System.map files and
output from "make scripts".

External module builds should either pass O= on the command line, or
set KBUILD_OUTPUT to point to the build-artifacts. module-base.bbclass
takes care of setting KBUILD_OUTPUT, so most existing external module
recipes are transparently adapted to the new source/build layout.

recipes that depend on the kernel source must have a depedency on the
do_shared_workdir task:

 do_configure[depends] += "virtual/kernel:do_shared_workdir"

With this dependency added, the STAGING_KERNEL_DIR will be populated and
available to the rest of the build.

Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 10 insertions, 2 deletions

diff --git a/meta/classes/module-base.bbclass b/meta/classes/module-base.bbclass
index 9537ba9f43..3eb2e9226e 100644
--- a/meta/classes/module-base.bbclass
+++ b/meta/classes/module-base.bbclass
@@ -3,16 +3,24 @@ inherit kernel-arch
 export OS = "${TARGET_OS}"
 export CROSS_COMPILE = "${TARGET_PREFIX}"
 
-export KERNEL_VERSION = "${@base_read_file('${STAGING_KERNEL_DIR}/kernel-abiversion')}"
+# This points to the build artefacts from the main kernel build
+# such as .config and System.map
+# Confusingly it is not the module build output (which is ${B}) but
+# we didn't pick the name.
+export KBUILD_OUTPUT = "${STAGING_KERNEL_BUILDDIR}"
+
+export KERNEL_VERSION = "${@base_read_file('${STAGING_KERNEL_BUILDDIR}/kernel-abiversion')}"
 KERNEL_OBJECT_SUFFIX = ".ko"
 
 # kernel modules are generally machine specific
 PACKAGE_ARCH = "${MACHINE_ARCH}"
 
+do_configure[depends] += "virtual/kernel:do_shared_workdir"
+
 # Function to ensure the kernel scripts are created. Expected to
 # be called before do_compile. See module.bbclass for an exmaple.
 do_make_scripts() {
 	unset CFLAGS CPPFLAGS CXXFLAGS LDFLAGS 
 	make CC="${KERNEL_CC}" LD="${KERNEL_LD}" AR="${KERNEL_AR}" \
-	           -C ${STAGING_KERNEL_DIR} scripts
+	           -C ${STAGING_KERNEL_DIR} O=${STAGING_KERNEL_BUILDDIR} scripts
 }